Citrobacter rodentium(ϕStx2dact), a murine infection model for enterohemorrhagic Escherichia coli

Abstract

The formation of attaching and effacing (A/E) lesions on intestinal epithelium, combined with Shiga toxin production, are hallmarks of enterohemorrhagic Escherichia coli (EHEC) infection that can lead to lethal hemolytic uremic syndrome. Although an animal infection model that fully recapitulates human disease remains elusive, mice orally infected with Citrobacter rodentium(ϕStx2dact), a natural murine pathogen lysogenized with an EHEC-derived Shiga toxin 2-producing bacteriophage, develop intestinal A/E lesions and toxin-dependent systemic disease. This model has facilitated investigation of how: (A) phage gene expression and prophage induction contribute to disease and are potentially triggered by antibiotic treatment; (B) virulence gene expression is altered by microbiota and the colonic metabolomic milieu; and (C) innate immune signaling is affected by Stx. Thus, the model provides a unique tool for accessing diverse aspects of EHEC pathogenesis.

Figure 1.. Insights provided by the C. rodentium(ϕStx2dact) murine infection model. (See text for additional details.)

(A) Prophage induction and phage gene expression, initiated by the SOS response, (depicted by the lightning bolt), which can be triggered by some antibiotics, leads to Stx production, bacterial lysis, and disease. Hence, mutation of C. rodentium genes required for the SOS response (e.g., recA) or ϕstx2_dact genes required for full expression of the stx genes (e.g., encoding the Q anti-terminator protein) drastically reduce Stx production in vitro and during infection [29]. Thus, a DNA gyrase inhibitor that diminishes the bacterial intestinal load but also induces the SOS response does not ameliorate disease. In contrast, antibiotics that clear C. rodentium(ϕStx2dact) without inducing the SOS response display efficacy in this model. (B) Microbiota- and host-derived metabolites regulate C. rodentium(ϕStx2dact) gene expression, thus facilitating environmental adaptation, colonization, and virulence. Virulence gene expression is enhanced (green arrow) by bacterial sensing of arginine; “Arg”. In contrast, the tryptophan metabolites indole, produced by microbiota, or serotonin, produced by enterochromaffin cells (“EC”), exert a negative regulatory effect (red “⊥”) on C. rodentium(ϕStx2dact) virulence. (C) Gram-negative bacteria produce outer membrane vesicles (“OMV”) that deliver LPS to the cytosol of macrophages (“Mφ”), triggering formation of the noncanonical inflammasome and initiation of innate immune signaling. This process is modulated (red “⊥”) by Stx via an unelucidated mechanism. (Created with BioRender.com)